A growing segment of the semiconductor business is high voltage/high power devices and integrated circuits. A critical element in this business is the power MOSFET. Power MOSFETs have many diverse applications in automotive, communications, consumer, data processing, industrial and military markets. For example, power MOSFETs may be used as drivers for motors, lamps, or displays. Most power MOSFETs are built in silicon. However, the performance of power MOSFETs built in silicon are already close to their theoretical limits. Therefore, research efforts have turned to silicon carbide (SIC) wafers. SiC has the potential for significantly (as much as two orders of magnitude) higher performance power MOSFETs compared to silicon wafers. However, one of the limitations in using SiC is that the wafer size is much smaller than present silicon wafers. SiC wafers have been limited to approximately 1 inch diameters. This inhibits their use or production in existing silicon wafer fabrication facilities built to handle large wafers.
Both depletion mode and inversion mode MOSFETs have been demonstrated in SiC. A depletion mode device is shown in FIG. 1a. The MOSFET channel was built in a 1.2 um thick n-type b-SiC epitaxial layer. A polysilicon annular gate electrode was used. Source/drain regions were implanted at 773K and contacted with tantalum silicide (TaSi2) which was annealed at 1173K. The depletion threshold voltage was -12.9 V and the device operated up to a drain voltage of 25 V at temperatures up to 923K. An inversion mode MOSFET is shown in FIG. 1b. A p-type b-SiC epitaxial layer was used. The threshold voltage was 9 V and the device operated up to 923K.